Horse smuggling exposes cracks in US defenses against screwworm

When sheriff's deputies intercepted a trailer carrying six horses near the border town of Redford, Texas, they uncovered more than a livestock violation.

The animals had crossed the Rio Grande illegally from Mexico through a shadowy smuggling network, bypassing the veterinary inspections, health certifications and quarantine measures that the US requires for livestock.

Smuggled animals are coming into focus as possible hosts for New World screwworm. The flesh-eating parasite began infesting US cattle in June despite efforts to halt the spread, such as a US ban of more than a year on Mexican livestock, a team of government inspectors on horseback and a swarm of sterile flies.

The horses caught near Redford in late May were not infested, but the case highlights a little-enforced part of the US response to the threat. As US authorities restricted cattle imports and disrupted billions of dollars in trade to contain the fly, a cartel-linked trade in horses and other animals continued moving through remote stretches of the border.

For more than a year, US officials have argued that illegal livestock trafficking from Central America helped carry screwworm north.

But Reuters found illicit animal movements have also persisted along parts of the US-Mexico border, often taking the same routes used to smuggle drugs and people.

The stakes are enormous. A previous screwworm outbreak killed thousands of animals in the US before the pest was declared eradicated in the 1960s.

In Texas, where authorities confirmed the first new US animal cases this year, experts estimate a widespread outbreak could cost the economy up to $1.8 billion.

The Trump administration has partially reopened the border to Mexican livestock to bring relief to US consumers, with beef prices at record highs after the ban, despite rising infestations in Mexico.

US Department of Agriculture officials, law enforcement and animal-industry experts said smuggled animals range from high-value horses bought for racing and rodeos to dogs used in illegal fighting rings and cattle. Authorities have also intercepted exotic animals, including primates, bears and tigers in recent years.

Mexico's animal health agency Senasica has confirmed over 2,000 equine cases of screwworm since the outbreak started in 2024.

"These kinds of movements represent a risk because they allow the fly to travel much faster than it could move naturally," said Oscar Rico, a researcher at Universidad Nacional Autonoma de Mexico, who co-authored a study predicting how animals could spread screwworm.

Border patrols reveal smuggling scale

During a week in August, Reuters visited three remote communities along the Texas-Mexico border, joined patrols with local officers and interviewed sheriffs, veterinarians and former Border Patrol agents.

They described the challenge of policing hundreds of miles of rugged terrain where animals, drugs and people can cross undetected.

Presidio County Sergeant Deputy Sheriff Jaime Sanchez, who investigated the Redford case, said trafficked horses can fetch at least $30,000 on the black market, with smugglers able to undercut legal sellers by avoiding import paperwork, taxes and veterinary requirements. Smugglers often take the horses to Houston and Dallas, where they sell them for farm work, racing or charrería, Mexico's traditional equestrian sport.

Sanchez's department has intercepted more than 50 smuggled horses in the past two years by pulling over horse trailers, an unusual sight in the dry, border community of Presidio, Texas.

Redford, historically known as "El Polvo" (the Dust), is a near-ghost town, with roads lined by abandoned homes and a shuttered school. With fewer than 20 families living there, the community has become a vulnerable corridor for illegal crossings controlled by Mexican cartels, where vast stretches of isolated terrain can provide cover, Sanchez said.

On a scorching day in August, he pointed to a shallow stretch of the Rio Grande where smugglers walked the horses across the river and through the private property of an older resident before loading them into a trailer.

 "It's easy for them to pay someone $500 or $1,000 per horse to cross it, load it onto the trailer, and drive off."

Presidio County Sergeant Deputy Sheriff Jaime Sanchez

Presidio County is working with federal officials to curb animal smuggling, which Sanchez attributed to La Linea, a cartel that the Trump administration designated a Foreign Terrorist Organization in July. The FBI also linked the group to criminal activity along the border.

"Since these are security matters, the issue of screwworm always comes up because it can hit economies very hard," Sanchez said. "In reality, we are very concerned."

Mexico's environmental regulator Profepa said in a statement that it cooperates with the US Fish and Wildlife Service to share information on "trafficking cases, coordinated enforcement operations, and the return or repatriation of live wildlife specimens."

Spokespersons for Mexico's security, agriculture and foreign ministries declined to comment.

Undocumented crossings evade inspections

US officials have not linked any of the country's 48 confirmed screwworm cases to smuggling. Many experts think that is likely an undercount since wildlife and smuggled animals evade scrutiny. The USDA has not identified how screwworm first reached the US, saying in a statement that epidemiological investigations are ongoing.

Scientists, veterinarians and epidemiologists interviewed by Reuters said undocumented animal crossings present the same types of disease-transmission risks that officials have linked to illegal cattle movements originating in Central America, because animals moving outside regulated channels may avoid inspections and treatment that could identify infections.

USDA Inspector General John Walk said the recent smuggling at the US southern border "seems more pronounced" and that animal trafficking is not just an agricultural concern, but a national security issue heightened by screwworm.

"It could be a vector," Walk said at his office in Washington, DC

In July, Walk traveled to Brownsville, Texas, to alert local law enforcement to the risk animal-trafficking networks pose of spreading screwworm. US Secretary of Agriculture Brooke Rollins said on X in early August that the department was "cracking down" on illicit livestock movements in a post about the US screwworm response.

Ricardo Ramirez, 57, has spent his life watching cattle roam across his sunbaked ranch in Zapata County, about 500 miles (805 km) southeast of Presidio, where his family has owned land since the 1940s.

Screwworm "didn't affect us for the last 50 years and lo and behold, here we are again with this thing upon us," Ramirez said from beneath the sparse shade of a tree on his ranch.

Focus on horse trailers

One August morning, Zapata came alive with the sound of engines, radios and speedboats. About 80 law enforcement officers with Operation Lone Star Task Force, a state law enforcement coalition to deter illegal crossings and smuggling, converged for a coordinated sweep. Patrol trucks rolled along highways and back roads, while officers searched waterways for signs of illegal activity.

Among the vehicles drawing investigators' attention are horse trailers, which blend into rural life.

Hours later, as Goliad County deputies launched a drone into the dark sky to scan remote areas along the border, they pointed to a 2024 case that they say demonstrates how smugglers can deploy trailers.

Officers stopped a livestock trailer and found 14 people inside, alongside a neglected horse. Investigators determined the vehicle was connected to human smuggling, and the driver told authorities he was paid $10,000.

"Most people, when they think about the cartel, they think about either drugs or illegal aliens," Goliad County Sheriff Roy Boyd said. "The revenue streams for the cartels are far more diverse than people have ever suspected."

In Terrell County, Texas, where the US-Mexico border cuts through rocky desert terrain, Sheriff Thaddeus Cleveland gestured from his pickup truck at a herd of feral cattle slowly crossing the river. Plastic water bottles and discarded clothing litter the landscape, traces of people who crossed the border illegally.

"A lot of times the smugglers would use horses to bring the drugs across the border due to the terrain," said Cleveland, a former Border Patrol agent, adding that the animals were often turned over to the USDA for mounted agents to use.

Animal-smuggling routes present a particular challenge for screwworm control because infected animals may never come into contact with veterinarians.

Tawnee Preisner, founder of the Tennessee-based Horse Plus Humane Society, said her organization has found horses with neck wounds, metal tracheotomy tubes and deep tissue pockets, raising concerns that smugglers may be hiding drugs or contraband inside the animals. The FBI contacted the organization in 2025 for information on horse smuggling, she said.

"When horses are being used to move drugs and humans, if a horse gets (screwworm), they're not going to report it," Preisner said, adding, "They're just going to shoot the horse, bury it and keep going."